1. Field of the Invention
The present invention relates to a laminated structure in which insulator layers and electrode layers are alternately stacked, and a method of manufacturing the laminated structure.
2. Description of a Related Art
Laminated structures in each of which insulator (dielectric) layers and electrode layers are alternately formed, are utilized, not only in laminated capacitors, but also in various other uses such as piezoelectric pumps, piezoelectric actuators and ultrasonic transducers. In recent years, with the developments of devices and equipment concerning MEMS (microelectromechanical systems), elements each having such a laminated structure have been microfabricated still further and packaged more highly.
In the microfabrication of an element which has opposing electrodes, decrease in the area of the element lowers the capacitance between the electrodes, so that the problem of rise in the electric impedance of the element occurs. When the electric impedance rises in, for example, a piezoelectric actuator, the impedance matching between the piezoelectric actuator and a signal circuit for driving this piezoelectric actuator cannot be established, and it becomes difficult to feed power to the piezoelectric actuator so that the performance of the piezoelectric actuator degrades. Further, in an ultrasonic transducer employing a piezoelectric element, the detection sensitivity for an ultrasonic wave degrades. For those reasons, in order to enlarge the capacitance between the electrodes while microfabricating the element, it has been practiced to alternately stack a plurality of piezoelectric material layers and a plurality of electrode layers. Thus, the capacitance between the electrodes of the whole element can be enlarged by connecting the plurality of stacked layers in parallel.
In such a laminated structure, interconnections are formed from the side surfaces of the laminated structure in order to connect the plurality of electrode layers to one another. FIG. 14 is a sectional view for explaining a conventional interconnection method for a laminated structure. The laminated structure 100 includes a plurality of piezoelectric material layers 101, a plurality of electrodes 102 and 103, and side electrodes 104 and 105. Each of the electrodes 102 and 103 is so formed that its one end extends to one wall surface of the laminated structure. Thus, the electrodes 102 are connected with the side electrode 104 and are insulated from the side electrode 105. Besides, the electrodes 103 are connected with the side electrode 105 and are insulated from the side electrode 104. A potential difference is afforded between the side electrode 104 and the side electrode 105, whereby the piezoelectric material layers 101 arranged between the electrodes 102 and the electrodes 103 are expanded or contracted by the piezoelectric effect.
Meanwhile, as shown in FIG. 14, insulating regions 106 where no electrodes are formed are provided in juxtaposition with the electrodes 102 and 103 in order to insulate these electrodes from the side electrodes 105 and 104, respectively. Unlike the other regions of the piezoelectric material layer 101, each of the insulating regions 106 is not expanded or contracted even when a voltage is applied between the electrode 102 and the electrode 103. This results in the problem that the part 106 undergoes stress concentration and is liable to damage.
As another interconnection method in a laminated structure, Japanese Patent Application Laid-open JP-P2002-118305A (p. 1, FIG. 1) discloses an interconnection method for a multi-electrode piezoelectric device with a piezoelectric/electrostrictive material, having a large number of electrodes which are individually controlled, comprising the steps of coating with an insulating material, part or all of an electric circuit board or an electronic circuit board in which the electrodes for external connections are formed on a surface of the piezoelectric/electrostrictive material, and removing the insulating material coated on desired electrodes for external connections to form interconnection patterns on the surface of the desired electrodes, thereby establishing conductions between interconnection lines and the desired electrodes. With such a method, however, it is complicated to form the interconnections for a large number of arrayed laminated structures, respectively. Especially in the case where laminated structures are arrayed in two dimensions, it is difficult to form the interconnections.